Current limiting lightning arrester using porous material in the gap structure



Sept. 29, 1964 Filed Dec. 27. 1961 flee V0175 J. H. SNELL, JR 3,151,274 CURRENT LIMITING LIGHTNING ARRESTER USING POROUS MATERIAL IN THE GAP STRUCTURE 2 Sheets-Sheet 1 \ONEPMTE/MPERV/MS' 0N6 P1975 Pom/s I I I I I 500 1000 1500 2000 2500 7/M //V M/CEO 5COND5 [pl/67226,:

James H Size/Z v/r,

A 56m v41? 150349720? Sept. 29, 1964 J. H. SNELL, JR 3,151,274

CURRENT LIMITING LIGHTNING ARRESTER USING POROUS MATERIAL IN THE GAP STRUCTURE Filed Dec. 27, 1961 2 Sheets-Sheet 2 United States Patent 0 CURRENT LIMITING LIGHTNING ARRESTER USING PGRGUS MATERIAL IN THE GAP STRUCTURE James H. nell, Jrz, Pittsfield, Mass, assignor to General Electric Company, a corporation of New York Filed Dec. 27, 1% Ser. No. 162,383 4 flaims. (6i. 315-46) This invention relates to a lightning arrester and, more particularly, to a current limiting lightning arrester using porous material in the gap structure.

In the lightning arrester field, the use of some type of spark gap construction in series with a type of non-linear resistance valve material is well known. The combination of the gaps and valve material is utilized to provide a path to ground for transient and surge voltages which may appear on an electrical conductor, where such voltages would be of sufiicient amplitude or strength to damage electrical equipment connected to the conductor. As is well known, the valve material presents a high resistance to the low voltages of the normal power line and lower resistance to the higher voltages, such as surge voltages, which the arrester is designed to conduct to ground to prevent damaging the electrical equipment connected to such power line. The gaps in general are over at a predetermined voltage level. This predetermined voltage level is set below the limit of transient or surge voltages which can be carried by the electrical conductor without damage to electrical equipment. In the normal construction of these arresters, the are within the gaps is caused to move into an arcing chamber associated with the gaps, to thereby increase the arc voltage. Of course, the main object of the arrester is to discharge these sudden surges, which may be lightning or switching surges. Obviously, after the surge has been dissipated it is desired that the arrester return to its open circuit condition to prevent the discharge of the normal line current, which is usually termed the power follow current, by the lightning arrester.

In many present day lightning arrester structures, a coil is provided in serieswith the sparking gap, such that when the coil is energized a flux is created which will aid in moving the arcs from the gap into the arcing chambers. One construction of such a coil is shown in Patent No. 2,566,895, issued September 4, 1951, to J. W. Kalb for Protective Device and assigned to the same as signee as this invention. As is well understood by those skilled in the art, these coils are generally shunted, either with a resistor or a gap, as a voltage limiting element to protect the coil from flashover and insulation damage due to the large voltage surges.

In the operation of lightning arresters, after the sudden surge has been discharged, the arcsare lengthened to thereby increase the arc voltage, which will limit the power follow current which flows in the lightning ar rester. It will be clear that the greater the resistance of the are that is maintained in the arcing chambers, the greater will be the voltage drop across such arcs. Clearly, the larger the chamber the longer will be the arc and thus the greater will be the arc voltage. However, it is desirable to provide a high arc voltage, while at the same time maintaining an arrester which is of sufliciently small size that it may be readily installed on an electrical power line near electrical equipment which requires protection from voltage surges.

It is, therefore, one object of this invention to increase the arc voltage within an arcing chamber Without increasing the size of such arcing chamber.

It is a further object of this invention to improve the efficiency of a lightning arresterwithout increasing the size or cost of such arrester.

A still further object of this invention is to provide a new and improved spark gap structure which will provide greater are voltages without increasing the size or cost of such structure.

Another object of this invention is to provide a spark gap assembly which will more rapidly build up are voltages within such assembly as compared to presently available spark gap assemblies.

It is still another object of this invention to provide an improved lightning arrester with a novel are gap structure whereby the arrester will be able to efl'iciently dissipate voltage surges which may be experienced on the electrical conductor connected to such lightning arrester.

In carrying out this invention in one form, a spark gap construction is provided comprising a pair of main electrodes and an intermediate electrode mounted in adjacent arc chambers. The are chambers are formed with outer plates of impervious material having an intermediate plate of porous material sandwiched between the outer plates, the porous plate functioning to increase the arc voltage within the chambers. The main electrodes are preferably mounted on the outer plates while the intermediate electrode straddles the porous material. A coil member may be provided connected in series circuit with the electrodes to move the are into the arc chambers.

In a lightning arrester made according to this invention, the gaps and coil are connected electrically in series with a non-linear resistance material so as to provide a lightning arrester which will substantially limit the current flow therethrough.

The invention which is desired to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its objects and advantages are obtained, as Well as other objects and advantages thereof, will be better understood from the following detailed description of a preferred embodiment thereof when considered in the light of the accompanying drawings, in which:

FIGURE 1 is an elevation view, partially in section, of one form of a lightning arrester made according to this invention;

FIGURE 2 is a top view, with portions broken away, showing one form of the novel spark gap assembly made according to this invention;

FIGURE 3 is an elevation view of the spark gap assembly taken on the line 33 of FIG. 2;

FIGURE 4 is an exploded perspective view of a portion of a gap assembly according to one form of this invention;

FIGURE 5 is an exploded perspective view of a portion of a gap assembly made according to another form of this invention;

FIGURE 6 is a perspective view of one form of electrode which may be used in the gap assembly shown in FIG. 5; and

FIGURE 7 is a graph comparing the build-up of arc voltages within a gap structure made according to this invention and a prior art gap structure.

Referring now to the drawings, in which like numerals are used to indicate like parts throughout the various views thereof, and in particular with reference to FIG. 1, there is shown a lightning arrester Ill. Arrester 10 comprises an annular, insulated outer member or casing 12 which may be for example, porcelain or the like, having an upper electrode or-terminal 14 which may be attached to a line electrical conductor such as 16, and having a lower electrode or terminal 18 connected to ground, as indicated. The upper terminal 14 is preferably a metallic member which is sealed to an opening within the casing 12 in any desired manner such as, for example, the gasket 7 2t), and is provided with a lower portion 22 which exenemas tends into the hollow interior of the casing 12. Within the outer member or casing 12 is mounted the component parts of the lightning arrester comprising the gap assembly 24, with a coil member 25, and a non-linear resistant valve material indicated at 26. A spring member 28 makes a firm electrical connection between the lower portion 22 of the terminal 14 and an upper metallic plate 30 which is electrically connected to coil member 25. The coil member 25 is electrically connected in series with the gap assembly 24. A lower plate 32 between gap assembly 24 and the non-linear valve resistant material 26 forms an electrical connection between the gap assembly 24 and the valve material 26. The lower end of valve material 26 is firmly seated on and makes electrical contact with a lower metallic member 34, which is in electrical contact with the bottom closure member 35. The terminal member 18 is electrically connected to member 36. As indicated, the member 34 is forced against the lower end of the casing 12 and is provided with a sealing means, such as gasket 38, to form a tight hermetic seal between the lower member 34 and the casing 12. The outer closure member 36 is firmly secured to the sides of the casing 12 as indicated by the peened over portions of the member 36. Thus there is provided a lightning arrester which is connected between a line terminal 16 and ground, such that a sudden lightning surge appearing on the line conductor 16 will cause the spark gap assembly 24 to are over, allowing the current to flow through the valve member 26 and the lower terminal 18 to ground. As is well understood, after the power surge has been dissipated the follow current, which then flows within the lightning an'ester 10, will be interrupted by the interaction of the spark gap assembly 24 and the valve member 26. The construction and operation of the spark gap assembly 24 is discussed in more detail in the following description.

Referring now to FIGS. 2 and 3 of the drawing, a preferred embodiment of a spark gap assembly is shown in detail. As there shown, the spark gap assembly 24 comprises an upper terminal or plate 31 and a lower terminal or plate 32, the plates being serially electrically connected, for example, by bolt means 34 to the upper and lower electrodes of the spark gap assembly 24. The main body of the spark gap assembly 24 comprises a number of blocks or plates of impervious material, shown for example as plates 36, 38, and 40, and having blocks or plates of porous material sandwiched therebetween, shown for example as plates 42 and 44. The various spark gap chambers for the spark gap electrodes within the spark gap assembly 24 are formed between an impervious block and a porous block, for example, between impervious block 36 and porous block 42. Of course, it will be understood, that in the usual manner as shown in FIG. 1 a coil member 25 will be provided with the spark gap assembly 24, so as to be energized by the current flowing through the spark gap assembly to provide the desired magnetic flux to cause movement of the are within the spark gap electrodes into the spark gap chambers.

It has been discovered that if porous material is utilized to form a portion of the spark gap chamber that a higher rate of increase in the arc voltage is obtained, as the arc proceeds along the spark gap electrodes and progresses outwardly into the arc gap chamber. This of course is very desirable in a current limiting arrester, since this is the basic means whereby the follow current is maintained at a low value and is interrupted each time the arrester is called upon to operate. Of course the increase in arc voltage will in turn permit a decrease in the amount of non-linear valve material which is required in the arrester. As will be apparent to those skilled in the art, the above two functions will permit lower IR voltages within the arrester than would be possible in the various arresters available in the prior art.

The higher rate of increase in arc voltage that is ohtained by using porous material in the spark gap chamber is clearly shown in FIG. 7.

The graph of FIG. 7 shows the substantially higher voltage increase that is possible by using a porous material in a portion of the spark gap chamber rather than the impervious material of the prior art. In FIG. 7 the lower curve shows the increase in arc voltage with respect to time of a spark gap or arcing chamber using impervious material. The test was performed using a magnetic field to move the are from between the electrodes into the arc chamber, using a test current of 1,000 amps. A second test was performed using the identical conditions, the only difference being that the arcing chamber was made with one plate of impervious material and one plate of porous material. The upper curve shows the results of this test. As can be seen, in less than 500 microseconds, the gap using an arc chamber with one porous plate had an arc voltage of 1800-1900 volts while the gap using an impervious arc chamber did not reach more than 800 Volts in a similar period. This test clearly shows the improved arc voltage which may be obtained by using the arc gap structure of this invention.

Referring again to FIG. 2, the top view of the spark gap assembly 24 is shown. in this view the top plate or terminal 31 is broken away at one end thereof and shows a main spark gap electrode 46 which is connected to the upper plate or terminal 31 by means of the bolt 34. An intermediate spark gap electrode 48 is also shown, fitting within a slot 50 of the porous plate 42. As indicated in FIG. 2, the intermediate electrode 48 is a T-shaped member having one portion 52 of the cross-member resting on the top of porous block 42. The other portion 54 of the cross-member is shown in dotted lines, indicating that it rests on the bottom of the porous block 42. Shown in FIG. 2 is a second main electrode 56, also shown in dotted lines, the second electrode 56 being connected to the next lower impervious plate, shown as 38 in FIG. 3. As shown in both FIGS. 2 and 3, the electrode 56 is connected to the impervious plate or block 38 by means of a bolt 58, which is also connected to another main electrode on the lower side of plate 38.

Of course, as will be understood, between impervious plates 38 and 40 is a second porous block 44, and mounted within the porous block 44 in the same manner indicated with reference to electrode 48 is a second intermediate electrode which provides the spark gap between the main electrode on the bottom of plate 38 and the main electrode on the top of the plate 40. From the above it is believed apparent that the spark gap assembly 24, as shown, includes four spark gap chambers. Four main electrodes are provided, two being connected to one of the blocks of impervious material, while the remaining two are each connected to a single block of impervious material. Also two intermediate electrodes are provided, each mounted on one of the blocks of porous material. This construction forms a spark gap assembly having a plurality of spark gap chambers, each chamber having as one side thereof a block of porous material. it will be obvious that the spark gap assembly could be provided with more or less spark gap chambers, if desired, using the same type of construction. It is only required that each chamher be provided with one porous plate, as indicated.

FIGURE 4 of the drawing shows an exploded, perspective view of a porous plate and an impervious plate along with the spark gap electrodes and the spark gap chamber formed therebetween according to the form of invention shown in FIGS. 2 and 3. Referring to FIG. 4, it is seen that the plates therein shown are the first. porous plate 42 and the centrally located impervious plate 38 of spark gap assembly 24. As shown, a spark gap chamber, indicated at 60, is formed between plates 42 and 38. The porous plate 42 is provided with a slot 56 into which is fitted the intermediate electrode 48. As can be more clearly seen in this view, the intermediate electrode 43 is formed in a T-shape, with the upper por- 2 6 tion 52 of the cross-member resting on the top of the porous block 42 while the lower portion 54 of the cross member rests on the lower side of the porous block 42. The imprevious block 38 is provided with the electrode 56, secured thereto by bolt means 58, and is provided with a depression in the center thereof which forms part of the spark gap chamber 60. The top of chamber 60 is formed by the porous block 42.

As will be apparent from FIG. 4, the intermediate electrode 48 fits within a channel 62 which is formed in the impervious block 38, suchthat the base of electrode 48 is maintained in the desired spark gap relation with the electrode 56, while the T-portion 54 fits into the portion of the channel 62 extending into the arc chamber 60. It will be noted that the portion of electrode 48, indicated at 54, is provided with a hook end and that the channel 62 is provided with a similarly shaped hook end. While this is not necessary, it has been found desirable, since it aids in maintaining the electrode 48 in the pre-set position such that jarring will not move it closer to electrode 56, thereby disrupting the desired arcing distance which has been pre-set between electrode 56 and electrode 48. As will be understood, when electrodes 48 and 56 are subjected to a voltage surge the arc gap between 56 and 48 is broken down and an arc formed therebetween. The

' arc is then caused to move along electrode 48 and out along the portion 54 of electrode 48 into the-arcing chamber 69, where its arc voltage is substantially increased, especially by means of the porous material 42 forming the top of the arc chamber 60.

As shown in FIG. 4, various gap vents 64 are provided from the arc chamber 60 to allow the ionized gas within the arc chamber 60 to be dissipated from the arc chamber. Of course, it will be understood that a large portion of the ionized gas enters the porous material 42 and is then substantially de-ionized. Therefore, under most circumstances the vents 64 will be unnecessary. However, they have been shown in the preferred embodiment since, in some types of protective devices, they are desirable in the spark gap assembly.

Of course, it will be understood that the lower portion of the impervious plate 38 is formed in a similar manner as shown on the upper portion. However, it will be understood that the chamber and the electrode are disposed in a dilferent area of the plate to minimize the possibility of any are flashover along the outside surfaceof the spark gap assembly 24. For example, the electrode on the lower portion of plate 38 would be displaced 90 from the electrode 56, whereby their ends, electrically connected by bolt 58, would be above one another but the arcing portions of the electrodes would be disposed 90 away from each other. While FIG. 4 shows a present preferred embodiment of the electrodes and the arcing chambers, it is to be understood that the particular shape of the chamber and of the electrodes may be changed, if desired, without substantially changing their desired function.

FIGURE 5 shows a modification of the form of plates and electrodes which may be used in the spark gap assembly 24. In FIG. 5, two plates of the spark gap assembly are shown, the top plate being a porous plate 42a and the lower plate being an impervious plate 38a. The porous plate 42a is provided with a slot 591: into which a T-shaped, intermediate electrode 48a is inserted. The T-shaped electrode 48a has a cross-member formed from an upper portion 52a and a lower portion 54a. As will be understood, in the manner similar to that described for FIG. 4, the electrode 48a, shown more clearly'in FIG. 6,

is inserted within the slot 5%, the upper portion 52a extendingacross the top of the plate 42a while the lower portion 54a extends along the bottom of plate 42a, in the manner indicated by the phantom lines in FIG. 5. The impervious plate 38a is provided with an arcing chamber 6%, the top of which is formed by the porous plate 42a and has at one portion thereof a main sparking electrode 56a, which is secured thereto by a bolt means 58a. As

6 shown, a channel 62a is provided, having a portion ex tending into the arcing chamber 60 for receiving the intermediate electrode 48a.

As can be seen from FIG. 5, the base of the electrode 4811: does not extend in arcing relation with the electrode 56a. In this particular embodiment, the main electrodes connected to the impervious plates are maintained in spark gap relation by bosses, such as boss 66, and complementary slots 68, in porous plate 42a. These main electrodes are the first to spark over when the spark gap assembly is subjected to a surge voltage. However, shortly after the main electrodes spark over the arc moves out from between the main electrodes. As the arc moves it is divided into two smaller arcs by means of the intermediate electrode 48a. One of the smaller arcs is formed between electrode 56a and intermediate electrode 48a, and extends into the arcing chamber 60a, along the lower portion 54a of the electrode 48a. As can be seen from FIG. 5, the portions of the porous plate 42a between slots 50a and 68 are provided with sloping faces 70 and 72. These faces slopein opposite directions, as is indicated by the sloped face 70, which extends from the lower side of the plate 42a to the upper side, and the sloped face 72 which extends from the upper side of the electrode to the lower side.

From the foregoing it will be apparent that as the main arc is divided by electrode 48a, one small arc is formed between 56a and 48a. This arc is guided by the slope 72 down into the arc chamber 60a along the portion 54a of electrode 48a. This small arc extends into arcing chambers 60 and its arc voltage is substantially increased due to the porous material 4211. In a similar manner, the are which is transferred from the second electrode to electrode 48a will be conducted along the slope 70 into the upper arcing chamber (not shown) along the 'upper portion 52a of the electrode 48a. In this manner, the are which is first drawn between the two electrodes on the impervious material (only one 56a of which is shown) will be divided into two short arcs by means of the intermediate arcing electrode 48a. These short arcs will then be conducted into the separate arcing chambers (only 60a being shown), and each of the shorter arcs will then be extended into an arcing chamber having one side formed of porous material, whereby the arcing voltage will be increased.

From the above description of the preferred embodiment, and a modification thereof, of the gap structure of this invention utilizing porous material as part of the arcing chamber it is believed that those skilled in this art will readily understand the operation and utility of the spark gap assembly herein disclosed. It should be understood that various changes may be made in the constructional details of this invention, such as the particular shape of the arcing chamber or the configuration of the electrodes, and the like, without departing from the spirit of the invention herein-before set forth. Therefore, while there has been shown anddescribed particular embodiments of the invention it will be obvious to those skilled electrically connected to each other, one end of said spark gap assembly being electrically connected to one terminal of said housing, one end of said non-linear valve material e'lectrically'connected to another terminal of said housing, said spark gap assembly comprising a plurality of spark gap chambers, each chamber having mounted therein arpair of arcing electrodes, each arc interruptingchamber being formed between a plate of impervious material and a plate of porous material, each plate of imprevious material having secured thereto an arcing electrode, an intermediate electrode mounted within said porous material, whereby an arc struck between an electrode connected to said impervious material and the intermediate electrode mounted on said porous plate will be conducted into said arcing chamber formed between said impervious plate and said porous plate.

2. A gap structure for a lightning a r-res'ter comprising an impervious block, a porous block, an arcing chamber formed between said porous block and said impervious block, a pair of electrodes, one of said electrodes being secured to said impervious block, the other of said electrodes being mounted within said porous block, said other electrode being provided with a portion extending into said arcing chamber, whereby an arc struck between said first and said second electrode will be drawn into said arcing chamber and its voltage will be substantially increased therein.

3. A gap structure for a lightning arrester comprising a pair of impervious blocks, a porous block fitting between said impervious blocks, first and second electrodes, each mounted on one of said impervious blocks, an intermediate electrode, said intermediate electrode fitting within said porous block, an arcing chamber formed between said first impervious block and said porous block, a second arcing chamber formed between said second impervious block and said porous block, said intermediate electrode having portions, one portion extending into one arcing chamber and a second portion extending into said second arcing chamber, said intermediate electrode acting with said first and said second electrode to conduct arcs into said arcing chamber, whereby said arcs are acted upon by said porous material to increase the arc voltage of such arcs.

- 4. A gap structure for a lightning arrester comprising a first and second block of impervious material, a porous block fitting between said first and said second blocks of impervious material, arcing chambers formed between said firstimpervious block and said porous block and between said second impervious block and said porous block, electrodes mounted on said first and said second impervious block, an intermediate electrode fitting in a slot within said porous block, said intermediate electrode being provided with extending portions, one portion fitting on the top of said porous block and the other portion fitting on the bottom of said porous block, sloping sides provided on said porous block in the vicinity of said slot, whereby an are drawn between one of said electrodes and said intermediate electrode will be conducted by one of said sloping sides to one of said arcing chambers and an are drawn between said other electrode and said intermediate electrode will be drawn by the other of said sloping sides into the other of Said arcing chambers.

References Cited in the file of this patent UNITED STATES PATENTS 2,000,719 Slepian et al May 7, 1935 2,783,336 Latour Feb. 26, 1957 2,825,008 Kalb Feb. 25, 1958 3,019,367 Kalb Jan. 30, 1962 3,069,589 Cunningham Dec. 16, 1962 

1. A LIGHTING ARRESTER COMPRISING A TUBULAR HOUSING OF INSULATING MATERIAL, A METALLIC TERMINAL AT ONE END OF SAID HOUSING, A SECOND TERMINAL AT THE OPPOSITE END OF SAID HOUSING, A SPARK GAP ASSEMBLY AND A NON-LINEAR RESISTANT VALVE MATERIAL POSITIONED WITHIN SAID HOUSING AND ELECTRICALLY CONNECTED TO EACH OTHER, ONE END OF SAID SPARK GAP ASSEMBLY BEING ELECTRICALLY CONNECTED TO ONE TERMINAL OF SAID HOUSING, ONE END OF SAID NON-LINEAR VALVE MATERIAL ELECTRICALLY CONNECTED TO ANOTHER TERMINAL OF SAID HOUSING, SAID SPARK GAP ASSEMBLY COMPRISING A PLURALITY OF SPARK GAP CHAMBERS, EACH CHAMBER HAVING MOUNTED THEREIN A PAIR OF ARCING ELECTRODES, EACH ARC INTERRUPTING CHAMBER BEING FORMED BETWEEN A PLATE OF IMPERVIOUS MATERIAL AND A PLATE OF POROUS MATERIAL, EACH PLATE OF IMPREVIOUS MATERIAL HAVING SECURED THERETO AN ARCING ELECTRODE, AN INTERMEDIATE ELECTRODE MOUNTED WITHIN SAID POROUS MATERIAL, WHEREBY AN ARC STRUCK BETWEEN AN ELECTRODE CON- 